Zircon refractory composition and method of making it



United States Patent ice g... 1, 1...

HRCON REFRACTORY COMPOSITION AND METHOD OF MAKING IT Donald E. Emhiser,Brackenridge, Pa., assignor to Pittsburgh Plate Glass Company, AlleghenyCounty, Pa., a corporation of Pennsylvania No Drawing. ApplicationDecember 30, 1954 Serial No. 478,903

14 Claims. (Cl. 106-57) This invention relates to zircon refractorycompositions and the method of making these compositions. This inventionespecially relates to zircon refractory compositions from whichrefractory articles can be made by slip casting.

Zircon is essentially zirconium silicate (ZrSiO The theore icalcomposition of zirconium silicate is 67.2% zirconia (ZrO and 32.8%silica ($0,). The high melting point of zircon and its relatively lowcoefficient of thermal expansion, as well as other physicalcharacteristics, make zircon a suitable refractory raw material.However, in the forming of refractory articles with zircon difliculty isencountered in the preparation of zircon slips. In the formation ofzircon slips by adding minus 325 mesh zircon totwater it was found thattoo much water was required to give a sufficiently low viscosity to themixture for casting by pouring. When mixtures containing 20 parts ormore of water per 100 parts of zircon were used for slip casting thezircon in the slip would not stay in suspension for a sufiiciently longtime for casting and the resulting unfired refractory body had highshrinkage and low strength.

It is an object of this invention to provide a zirconcontainingcomposition suitable for forming a slip that can be cast and dried toform refractory articles having satisfactory structural strength beforeand after firing.

It is another object of this invention to provide a zircon slip with asufficiently low viscosity to be suitable for casting and yet containonly a small amount of water.

It is a further object of the present invention to provide a zircon slipin which a substantial portion of the zircon has an average particlesize greater than 44 microns.

It is still a further object of this invention to provide a zircon sliphaving a maximum of about parts of water per 100 parts of zircon and yethave quick-setting characteristics for solid casting.

Still a further object of this invention is to provide a method for theformation of the zircon-containing compositions and zircon slips of theforegoing objects.

These and other objects will be apparent to one skilled in the art fromthe description which follows.

g I have found that, when a small amount of sodium sm- '=cate, whichcontains 6 to 10% by weight so rum oxide and the weight ratio of sodiumoxide to silica is between 1:3 and 1:4, is used with zirco and wat toprepare the zircon slip, satisfactory slips are obtained using between 9and 18 parts of water per 100 parts of zircon. Examples of commercialsodium silicates which can be used as the sgdimn fligate for the zirconslips of the present invention are: sodium silicate containing 6.7% NaO, 25.3% Si0 and the balance water and having a density of 130* (33.5Baum); sodium silicate containing 8.9% Na- O, 28.5% SiO and the balancewater and having a density of 139+ (41.1. Baum); and sodium silicatecontaining 9.1% Na O, 29.3% SiO, and the balance water and having adensity of l.4l+ (42.2 Baum).

The amount of the sodium silicate usgcLcan be varied the amount of waterused is of the order of 9 to 10 parts of water to parts of zircon, 0.002to 0.03 part of a material capable of providing divalent metal cationsin the water per 100 parts of zircon is used along with the sodiumsilicate to provide a zircon slip suitable for solid casting. In thezircon-slips of the present invention the zircon, sodium silicate, waterand material capable of providing divalent metal cations constitutegreater than 99% of the composition.

The sodium silicate can be incorporated in the zircon slip in severalways. Sodium silicate in the recited proportion can be mixed with zirconand the mixture then mixed with water to form the slip. In anothermethod of forming the slip the zircon and water are mixed and whilemixing sodium silicate is added. In another method the sodium silicateis dissolved in the water of the slip composition and this solution isthen mixed with zircon to form the slip.

The amount of sodium silicate is dependent upon the method of castingfor which the zircon slip is to be used. When using drain'casting theamount of sodium silicate is 0.1 to 0.2 part per 100 parts of zircon andin order to obtain a slip having satisfactory characteristics, such aslow viscosity, the amount of water is 14 to 18 parts .per 100 parts ofzircon. If more than 18 parts of water is used, the slip is too thin sothat the final product after casting and drying does not have sufficientstructural strength. To obtain the best refractory article the watercontent should be 14 to 15 parts of water per 100 parts of zircon.

When using solid casting for the production of massive zircon refractorybodies, it was found possible to reduce considerably the amount of waterused. To permit water reduction the sodium silicate content must be inthe range of from 0.05 to 0.1 part and preferably 0.08 to 0.1 part per100 parts of zircon. In order to rovi k settin of this zircon slip, inwhich 9 to 10 parts of water per 100 parts of zircon is used, it wasfound necessary to inco orate in the zircon sli a mat erjal cgpablgqtzpfrblviding diva cut me a cations n tlie water. Such materials in ecompoun lCh are slightly soluble in water, such as alkaline earth metaloxide, as well as materials which are on y very 1g y so u g in water.Examples of alkaline earth metal oxides whichare used to providedivalent metal cations are li oxiMgJImnI-moxide. type of material isPortlitld gm Dicalcium j|icate, which is an essen1 constituent of Portand cement, 18

another example of a material capable QLPI'Ol/idiflg parts of zircon isused. Portland cemen nd similar materials uch as die lci 1 e are used insuc zircon slips for solid cas mg in an amount between 0.01

and 0.03 part per 100 parts of zircon. In all of the zircon slips forsolid casting 0.05 to 0.1 part of sodium silicate and 9 to 10 parts ofwater per 100 parts of zircon are used. The amount of lime is preferably0.009 part per 100 parts of zircon and the preferred amount of Portlandcement is from 0.02 to 0.03 part per 100 parts of zircon. In suchpreferred compositions from 0.08 to 0.1 part of sodium silicate per 100parts of zircon is used.

In zircon slip compositions containing the specified amounts of sodiumsilicate and Portland cement gphm' e more than 10 parts of water perparts of zircon re- EXAMIN sults in a cavity in the cast article. Forexample, a slip containing 11 parts of water per 100 parts of zircon wasunsatisfactory.

In slip casting heretofore carried out using zircon slips the slipscontained 16 to 17 parts of water per 100 parts of zircon. Articles madeby solid casting and using the zircon slips of this invention in whichthe water content is between 9 and 10 parts of water per 100 parts ofzircon exhibit considerably less shrinkage in the drying step. Thisreduced shrinkage resulted in cast bodies having shapes and dimensionsmore nearly representative of the mold and cast bodies can be obtainedessentially free of cracks.

From the foregoing description of the zircon slips of the presentinvention it is apparent that there are two classes of zircon slipcompositions recited, namely, those suitable for drain casting and thosesuitable for solid casting. In the former the amount of sodium silicateused is 0.1 to 0.2 part of sodium silicate per 100 parts of zircon whilein the latter slip composition the amount of sodium silicate is 0.05 to0.1 part, so that the range of 0.05 to 0.2 part covers the compositionswithout any gap. However, in the case of the water content it is to benoted that the former type of zircon slip utilizes 14 to 18 parts ofwater per 100 parts of zircon while in the zircon slips for solidcasting the range is from 9 to 10 parts of water per 100 parts ofzircon. Thus it is seen that there is a gap between the two ranges and,of course, the appropriate range is chosen in accordance with the typeof casting to be used. It is also apparent from the foregoing that, whensolid casting is to be the casting method, a material such as Portlandcement or lime is to be incorporated in the zircon slip to produce aslip with a satisfactory setting time and it is necessary to reduce theamount of sodium silicate to the range of 0.05 to 0.1 part per 100 partsof zircon.

In the foregoing description of the zircon slips for drain casting itwas mentioned that the water content can be between 14 and 18 parts per100 parts of zircon. When the zircon is substantially entirely pf amaterial which is minus 325 mesh, that is, has an average particle sizeof less than 44 microns, the amount of water necessary for producing asatisfactory zircon slip is of the order of 17 to 18 parts per 100 partsof zircon. It was found that it was possible to use granular zircon withthe finely ground or milled zircon, the latter being the aforesaid minus325 mesh zircon. When the amount of granular zircon, that is, a materialhaving an average particle size greater than 44 microns, is used in anamount of about 10 or 20% of the zircon content the water 5 content canbe reduced to as low as 14 parts per 100 parts of zircon and stillproduce a satisfactory zircon slip.

For zircon slips of this invention which are suitable for solid castingand in which materials capable of producing divalent metal cations inthe water, such as Portland cement and lime, it is necessary to use onlya sodium silicate content between 0.05 and 0.1 part per 100 parts ofzircon as mentioned above. No more than 10 parts of water per 100 partsof zircon is used; otherwise, the desired setting characteristics is notobtainable even with adjustment of the sodium silicate content. Thezircon of these slips for solid casting preferably contains 20 to 60%granular zircon and 40 to 80% milled zircBn to produce refractory bodieshaving improved structural strength. For best results the zircon is atleast 40% granular and the balance is milled zircon.

Using the suitable zircon slips described above for drain casting it hasbeen found possible to drain cast three-inch crucibles having wallthickness up to about three-quarters of an inch. The drain casting ofthreeinch crucibles having a wall thickness of about onequarter of aninch was quite easily accomplished. In order to prevent sticking indrain casting it was found necessary to completely dry the molds betweencastings.

Using the suitable zircon slips described above for solid casting anumber of eight-inch pots were successfully cast. In these castingoperations it was found that it was not necessary to dry the moldsbetween castings and,

as a matter of fact, slightly damp molds were found to be advantageous.The procedure for producing eight-inch pots comprised pouring thecorrect amount of slip into the mold, inserting the core and leaving itin place for twenty minutes. After the twenty minutes the slip has setsufficiently to allow removal of the core without danger of the potslumping. The core was then removed; otherwise, the set zirconcomposition would shrink around it sufficiently to make later removalimpossible. Refractory blocks as large as 4" x 6" x 10" were easilyfabricated from the zircon slip by solid casting.

In the following examples of production of satisfactory crucibles usingzircon slips suitable for either drain casting or solid casting, thezircon used was either milled zircon alone or a mixture of milled zirconwith granular zircon. Both of these zircons have approximately the samechemical composition and differ only in particle ypical chemicalanalysis was 65.03% ZrO,,

t (,0 33.9% 0.76% Ago 0.07% mo 0.17% TiO 0.04% CaO, 0.001% Cr O 0.17% P0 and 0.05%

alkali metal oxides. Milled zircon was 99.9% minus 325 mesh, whilegranular zircon was 74.7% on 140 mesh, 24.7% through 140 mesh and on 180mesh and 0.6% through 180 mesh. Thus it is seen that milled zircon hasan average particle size less than 44 microns, that is,

it is minus 325 mesh material, while granular zircon has an averageparticle size greater than 44 microns.

The amounts of materials expressed in this applicati on are parts byweight per 100 parts by weight of zircon.

Example I A zircon slip was prepared using 100 parts of milled zirconand 0.18 part of sodium slicate and 18 parts of water. The sodiumsilicate used in this and subsequent examples contained 6.7% N330, 25.3%SiO, and the balance water and had a density of 130+. The zircon slipwas used by drain casting to form a three-inch zircon crucible. The slipwas poured in a plaster of Paris mold. After a layer of zircon of thedesired thickness had formed against the mold, the excess slip waspoured out. The molded crucible was removed from the mold, dried andfired at a temperature of about 2650 F.

Example 11 A three-inch crucible was prepared by drain-casting, dryingand firing as in Example 1 except the zircon slip contained 0.1 part ofsodium silicate and 14 parts of water per 100 parts of zircon. Inaddition the zircon was 10% granular zircon and milled zircon.

Example III A satisfactory crucible was prepared as in Example II usinga mixture of 20% granular and 80% milled zircon. The slip contained 0.15part of sodium silicate 5 and 15 parts of water per parts of zircon.

Example IV A zircon slip was prepared using 80% milled zircon and 20%granular zircon. The slip contained 0.1 part as of sodium silicate,0.025 part of Portland cement and 9 parts of water per 100 parts ofm'rcon. The Portland cement used in this and two of the subsequentexamples shaped in the form of an eight-inch pot was allowed to dry andthe dried pot was fired at 2650' F.

Example V An eight-inch crucible was made in accordance with the processdescribed in Example IV using a zircon slip in which the zircon was 30%granular and 70% milled and in which 0.087 part of sodium silicate, and0.025 part of Portland cement were used along with parts of water per100 parts of zircon.

Example VI Example VII In this example a crucible was prepared inaccordance with the method described in Example IV and the zircon sliphad the same composition as described in Example V except that thezircon was 40%, granular and 60% milled.

In the manufacture of crucibles or pots for melting glass usingrefractory materials heretofore used it was necessary to choose amaterial in the form of a slip which as a cast pot would have its innersurface shrink away from the core and its outer surface at the same timeshrink away from the outside mold. This concurrent shrinkage would occurfor only a brief interval of time and then the entire composition wouldbegin to shrink in a conventional manner with all the dimensionsbecoming progressively smaller. It is during the concurrent shrinking ofthe outer surface from the pot mold and the inner surface from theplaster core that the slip changes from a fluid to a set state and therefractory pot is thereby slip cast off the pot mold. With zircon slipshaving compositions other than the zircon slips of the invention, thefailure in the formation of the pots was due to vibrations that were setup as the refractory pots were slip cast off the mold. With zircon slipsof this invention failure of the pot during formation due to vibrationalshock was minimized and it was even possible to use granular materialwith milled zircon in the slip composition. From Example VII it is seenthat a satisfactory crucible can be made using 40% of the zircon in agranular form.

Pots free of defects and highly resistant to thermal shock have beenmade by the solid casting method described above using zircon that wasup to 60% zircon having an average particle size greater than 44microns, i.e., using the granular zircon referred to above. The slipscontained sodium silicate and either Portland cement or lime in amountsin accordance with the slip compositions of this invention. By usingthese large amounts of granular zircon a more economical refractory bodyis obtained because granular zircon is considerably cheaper than milledzircon. In addition, the refractory articles with large amounts ofgranular zircon have greater resistance to thermal shock.

The zircon crucibles or pots made in accordance with the presentinvention are suitable for the manufacture of various glasses includingphosphate glasses. Zircon refractory bodies made in acocrdance with thisinvention include blocks and slabs for glass tank furnaces.

Three sets of zircon bars 1" x 1" x 4%" were prepared by solid castingand drying. For each set three bars were prepared. In the first set thezircon slip had the composition of Example IV. The second set had thecomposition of zircon slip in Example V while the zircon slip of thethird set used the composition of Example VII. The three bars of a setwere fired to different temperatures and then tested for modulus ofrupture. The following values were obtained:

While each of the bars in an unfired condition had a very low modulus ofrupture, the bars after firing at all three temperatures each had a veryhigh modulus of rupture and the values of the fired bars are greaterthan that ob tained by many refractory materials.

The foregoing are specific examples of the compositions of thisinvention for drain casting and solid casting and the method of makingthe same. These examples are presented for purposes of illustration andnot by way of limitation. The invention is not to be limited exceptinsofar as stated below in the claims.

I claim:

1. A fluid composition suitable for forming refractory articlesconsisting essentially of zircon, 0.05 to 0.1 part of sodium silicate, 9to 10 parts of water and 0.002 to 0.03 part of a material capable ofproviding alkaline earth metal cations in said water per 100 parts ofzircon, said sodium silicate containing 6 to 10% by weight of sodiumoxide and the weight ratio of sodium oxide to silica being between 1:3and 1:4.

2. A fluid composition suitable for forming refractory articlesconsisting essentially of zircon, 0.05 to 0.1 part of sodium silicate, 9to 10 parts of water and 0.002 to 0.015 part of an alkaline earth metaloxide per 100 parts of zircon, said sodium silicate containing 6 to 10%by weight of sodium oxide and the weight ratio of sodium oxide to silicabeing between 1:3 and 1:4.

3. The fluid composition of claim 2 wherein the alkaline earth metaloxide is lime.

4. The fluid composition of claim 3 wherein the lime is present in anamount of about 0.009 part per 100 parts of zircon.

5. A fluid composition for forming refractory articles consistingessentially of z' n, 0.05 to 0. art of sodium silicate, 9 to 10 arts 0an 0.01 art of silicate containing 6 to 10% by weight of sodium oxide ane we 0 0 so i "oxide to silica Being between 1:3 and 1:4.

v 6. A fluid composition suitable for forming refractory articlesconsisting essentially of zircon, 0.08 to 0.1 part of sodium silicate, 9to 10 parts of water and 0.002 to 0.015 part of lime per 100 parts ofzircon, said zircon comprising 20 to 60% zircon having an averageparticle size greater than 44 microns and 40 to zircon having an averageparticle size less than 44 microns and said sodium silicate containing 6to 10% by weight of sodium oxide and the weight ratio of sodium oxide tosilica being between 1:3 and 1:4.

7. A fluid composition suitable for forming refractory articlesconsisting essentially of zircon, 0.08 to 0.1 part of sodium silicate, 9to 10 parts of water and 0.01 to 0.03 part of Portland cement per partsof zircon, said zircon comprising 20 to 60% zircon having an averageparticle size greater than 44 microns and 40 to 80% zircon having anaverage particle size less than 44 microns and said sodium silicatecontaining 6 to 10% by weight of sodium oxide and the weight ratio ofsodium oxide to silica being between 1:3 and 1:4.

8. The method of preparing a fluid composition suitable for formingrefractory articles comprising forming a mixture consisting essentiallyof zircon, 0.05 to 0.1 part of sodium silicate, 9 to 10 parts of waterand 0.002 to 0.03 part of a material capable of providing alkaline earthmetal cations in said water per 100 parts of zircon, said sodiumsilicate containing 6 to 10% by weight of sodium oxide and the weightratio of sodium oxide to silica being between 1:3 and 1:4.

9. The method of preparing a fluid composition suitable for formingrefractory articles comprising forming a mixture consisting essentiallyof zircon, 0.05 to 0.1 part of sodium silicate, 9 to 10 parts of waterand 0.002 to 0.015 part of an alkaline earth metal oxide per 100 partsof zircon, said sodium silicate containing 6 to 10% by weight of sodiumoxide and the weight ratio of sodium oxide to silica being between 1:3and 1:4.

10. The method of claim 9 wherein the alkaline earth metal oxide is limeand is present in the amount of about 0.009 part per 100 parts ofzircon.

11. The method of forming a fluid composition suitable for formingrefractory articles comprising forming a mixture consisting essentiallyof zircon, 0.05 to 0.1 part of sodium silicate, 9 to 10 parts of waterand 0.01 to 0.03 part of Portland cement per 100 parts of zircon, saidsodium silicate containing 6 to 10% by weight of sodium oxide and theweight ratio of sodium oxide to silica being between 1:3 and 1:4.

12. The method of forming a zircon refractory body which comprisesforming the fluid composition of claim 1, casting a quantity of thefluid composition to produce a shaped body, drying the shaped body andthen firing the dried body.

13. The method of forming a zircon refractory body which comprisesforming the fluid composition of claim 5, casting a quantity of thefluid composition to produce a shaped body, drying the shaped body andthen firing the dried body.

14. The method of forming a zircon refractory body which comprisesforming the fluid composition of claim 7, casting a quantity of thefluid composition to produce a shaped body, drying the shaped body andthen firing the dried body.

References Cited in the tile of this patent UNITED STATES PATENTS1,375,077 Buckman Apr. 19, 1921 2,277,705 Kinzie Mar. 31, 1942 2,338,209Smith Jan. 4, 1944 2,373,864 Wainer Apr. 17, 1945

1. A FLUID COMPOSITION SUITABLE FOR FORMING REFACTORY ARTICLE CONSISTINGESSENTIALLY OF ZIRCON, 0.05 TO 0.1 PART OF SODIUM SILICATE, 9 TO 10PARTS OF WATER AND 0.002 TO 0.03 PART OF A MATERIAL CAPABLE OF PROVIDINGALKALINE EARTH METAL CATIONS IN SAID WATER PER 100 PARTS OF ZIRCON SAIDSODIUM SILICATE CONTAINING 6 TO 10% BY WEIGHT OF SODIUM OXIDE AND THEWEIGHT RATIO OF SODIUM OXIDE TO SILICA BEING BETWEEN 1:3 AND 1:4